Avalanche photodiode detectors (APDs) are photosensitive devices that detect optical power by converting an input signal (photons) to an electrical signal. The input signal is amplified by an “avalanche effect” when carriers are injected in an area with high electrical field. This occurs because multiple electron-hole pairs are created for each absorbed photon.
An APD typically comprises of a plurality of stacked layers including a multiplication layer and an absorption layer on a semiconductor substrate. The absorption layer absorbs incident photons to create electron/holes that are transferred to the multiplication layer. The multiplication layer multiplies the electrons/holes. This occurs when electron/holes have sufficient energy to create a new electron and hole. Initial carriers and newly created carriers may create additional electrons and holes (hence the name “avalanche”) by repeating the multiplication process.
In a conventional APD, all layers are grown in one epitaxial growth. This may lead to some interface defects. Due to interface defects there may be some carrier traps and recombination centers, which reduce overall quantum efficiency and after pulsing performance of an APD.
Furthermore, simultaneous growth absorption and multiplication layers does not provide flexibility in selecting different materials for these layers.
Therefore there is a need for an avalanche photodiode that overcomes the foregoing problems in conventional APDs.